Text Processing & Regular Expressions

Grep

grep "keyword" file.txt
grep "^keyword" file.txt # ^ will find your keyword that starts with the line
grep -i "keyword" file.txt # Makes it case insenstive
grep -n "keyword" file.txt # returns back which line your keyword was found.
grep -C 1 "keyword" file.txt # Gives the line before and the line after your keyword.
grep -v "someword" file.txt # Gives back patterns that dont match yours.
grep "Dev[To]*" file.txt # Finds all dev and devto and devt etc.
grep "^[1234567890]" file.txt # finds all lines starting with a number.
grep "[@qwertyuiopasdfghjklzxcvbnm].com" file.txt # finds all emails. 

SED

sed 's/Yo/Sup/' file.txt # Replaces first occurrence of Yo with Sup.
sed 's/Yo/Sup/g' file.txt # Replaces all matching on each line.
sed -i's/Yo/Sup/g' file.txt # This will modify the file. The other ways only modify what is show in the terminal.
sed '3d' file.txt # Deletes the 3rd line in the file
sed '1i\First line' file.txt # Adds the text "First line" to the file.txt
sed '$a\Last line' file.txt # Adds the text "Last line" to end of the file.
sed -e 's/Yo/Sup/g' -e 's/joshua/Joshua/g' file.txt # -e allows for mutiple commands.
sed 's/[Ww]orld/Galaxy/g' file.txt # RegEx finds any World or world and replaces with Galaxy.

AWK

awk '{print $1}' file.txt # Prints the first word of each column
awk '{print $1, $2}' file.txt # Prints the first and second word of each line
awk '$2 > 28 {print $1 " is over 20"}' file.txt # Looks at second word of each line and compares it to see if its greater than 28 then print it.
awk 'NR > 1 {sum += $2} END {print "Average age:", sum/(NR-1)}' awk_test.txt # Checks if name records is greater than 1.